As a power source system of this type, Japanese Patent Laying-Open No. 2010-259274 (Patent Document 1) discloses a power storage device charging pack having an external charging function and an external power supplying function, for example. The external charging function is of charging a high-voltage power storage device by receiving AC power from a commercial power source external to the vehicle and converting the AC power to DC power. The external power supplying function is of converting DC power of the high-voltage power storage device to AC power and supply the AC power to an external AC load when the AC load requests AC power. This power storage device charging pack includes: a high-voltage connection terminal connected to a high-voltage circuit that sends and receives high-voltage power; an external connection terminal connected to an external commercial power source or an external AC load; a system main relay unit provided between the high-voltage power storage device and the high-voltage connection terminal; a switching relay unit for switching connection of the high-voltage connection terminal or the external connection terminal to the high-voltage power storage device; and an AC/DC bidirectional charger capable of bidirectional conversion between AC power of the AC load and DC power.
According to Patent Document 1, the system main relay unit includes: a positive electrode side relay; a negative electrode side relay; and a precharging relay unit in which a precharging relay and a precharging resistor are connected in series. The switching relay unit further includes a positive electrode side switching relay and a negative electrode side switching relay. When externally charging the high-voltage power storage device or when externally supplying electric power from the high-voltage power storage device, the relays in the system main relay unit are disconnected and the positive electrode side switching relay and the negative electrode side switching relay are connected in the switching relay unit. During the external charging, AC power from the external commercial power source is converted into DC power by the AC/DC bidirectional charger, and is directly supplied to the high-voltage power storage device via the switching relay unit. Meanwhile, during the external power supply, DC power of the high-voltage power storage device is converted into AC power by the AC/DC bidirectional charger, and is supplied to the external AC load via the switching relay unit.